It has been known heretofore to incorporate into a traffic light various means for indicating the time left for illumination of a traffic light signal of one color before switching to a traffic light signal of another color.
For example, U.S. Pat. No. 4,255,737 issued in 1981 to R. Casteel teaches a traffic light apparatus that has a four sided housing, each side of which contains red and green areas that can be illuminated. Furthermore, each side contains a rotating semicircular mask which simultaneously and progressively covers one portion of one of the colored areas and uncovers a portion of the other colored area until the illumination of the traffic light is changed thereby causing a change in traffic flow. The rotation of the masks together with the actuation of the various lights is controlled from a common ring gear disposed within the housing and driven by a single motor. A disadvantage of this device is that it incorporates the traffic light covering/uncovering means directly into the traffic light apparatus. In other words, for introducing such a device into practice, it would be required to replace all existing conventional traffic lights, which is not only expensive but may increase the occurrence of accidents because of confusion caused by new appearance of the traffic lights. Another disadvantage of the aforementioned traffic light apparatus is that it has a complicated mechanical construction with a plurality of interconnected moving parts. These parts operate synchronously and simultaneously in four opposite directions. Traffic light apparatuses of this type are intended to be suspended from a console or another type support above the center of the intersection. However, in a majority of cases traffic lights of such types have been replaced by apparatuses installed on the corners of the street crossings and having signals facing only the oncoming traffic. Therefore the aforementioned device of U.S. Pat. No. 4,255,737 may find only an extremely limited practical application. Furthermore, this apparatus is not applicable to intersections which require different traffic signals for vehicles going in mutually opposite directions, e.g., a red light in one direction and a left turn/green light for the vehicle going in the opposite direction. It would be very difficult to adjust and change the mode of operation in the above-described apparatus.
U.S. Pat. No. 4,590,455 issued in 1986 to G. Fritzinger teaches a traffic control system that has green and/or red signal lights blinked momentarily at a predetermined interval before the direction of traffic is changed. A marker is placed along the roadway at a normal distance of travel within the timing of the blink signal to enable motorists to gauge their driving to save gasoline and achieve greater safety solely by noting their location relative to the marker when the blink signal occurs. Further taught is the use of the traffic signaling system in connection with a semi-actuated controller that has a synchronizer providing a background cycle. The timing of the blink signal and the yellow caution signal is obtained from the synchronizer. A disadvantage of this device is that blinking of the green signal may cause confusion, whereas blinking of the red signal is already equivalent to a stop signal and may not be understood as an indicator of the approaching switch in the traffic direction. Furthermore, an addition of a marker on the road at the approach to the traffic light may distract the driver's attention.
U.S. Pat. No. 5,726,648 issued in 1998 to M. Soon describes a time indicating traffic light that includes a vertically-oriented and rectangular-parallelepiped-shaped housing, a circular-shaped "stop" indicator light, a circular-shaped "caution" indicator light, seven rectangular-shaped "go" indicator lights, and a time indicating display. The circular-shaped "stop" indicator light, the circular-shaped "caution" indicator light, and the seven rectangular-shaped "go" indicator lights are disposed in the vertically-oriented and rectangular-parallelepiped-shaped housing. The seven rectangular-shaped "go" indicator lights have a pair of parallel, elongated, spaced-apart, vertically-oriented, and rectangular-shaped "go" indicator lights, and five adjacent, slightly vertically spaced-apart, horizontally-oriented, and rectangular-shaped "go" lights. The five adjacent, slightly vertically spaced-apart, horizontally-oriented, and rectangular-shaped "go" lights extinguish progressively upwardly towards the circular-shaped "caution" indicator light at a predetermined rate determined by a timer while the pair of parallel, elongated, spaced-apart, vertically-oriented, and rectangular-shaped "go" indicator lights remain illuminated when at least one light of the five adjacent, slightly vertically spaced-apart, horizontally-oriented, and rectangular-shaped "go" lights is illuminated. The time indicating display is disposed on the vertically-oriented and rectangular-parallelepiped-shaped housing and provides a visible display of the time of illumination of the seven rectangular-shaped "go" indicator lights, so that an approaching vehicle can determine when the circular-shaped "caution" indicator light will be illuminated by dividing the time of illumination on the time indicating display by the number of lights of the five adjacent, slightly vertically spaced-apart, horizontally-oriented, and rectangular-shaped "go" lights extinguished and thereby prevent sudden acceleration followed by a sudden stop.
A disadvantage of this timer indicating traffic light consists in that it is based on an entirely new conception and would require replacement of all existing traffic light units. Another disadvantage is that the device has a rather complicated construction, and therefore is expensive to manufacture. A provision of several different rectangular-shaped "go" indicator lights would require an essential increase in the overall dimensions of the traffic light assembly, as it would be necessary to make each "go" indicator light and the digital indicator visible from a far distance. A driver may need time for obtaining, processing the information indicated by the complicated traffic light system, and for making a decision. All this has to be done immediately, which may not be feasible for an elderly people whose driving ability would be limited.